fix bug in applying patches

When restarting a patch from crashing in the middle of a large file,
we're not finding the correct patch to apply to the copy saved in
cache.

Change-Id: I41cb2b87d096bb7a28a10c4cf3902facd45d4c9d
diff --git a/applypatch/applypatch.c b/applypatch/applypatch.c
index 3c816c5..b85b915 100644
--- a/applypatch/applypatch.c
+++ b/applypatch/applypatch.c
@@ -588,7 +588,7 @@
 
         int to_use = FindMatchingPatch(copy_file.sha1,
                                        patch_sha1_str, num_patches);
-        if (to_use > 0) {
+        if (to_use >= 0) {
             copy_patch_value = patch_data[to_use];
         }